55 ILCS 5/3-5014
Upon receipt of any mortgage, trust deed or conveyance of personal property having the effect of a mortgage or lien upon such property, upon which is indorsed the words, "this instrument to be filed, but not recorded" or words of a similar import, signed by the mortgagee, the mortgagee's agent or attorney, and upon payment of a fee equal to what would be charged if the document were to be recorded, the recorder shall mark the instrument "filed", endorse the time (including the hour of the day) of the receipt thereof and file the same in the office.
Each instrument filed as above shall be numbered and indexed by the recorder in the book wherein the recorder alphabetically indexes chattel mortgages and shall refer to the number appearing on the filed instrument.
The recorder may destroy any instrument filed but not recorded in the manner hereinabove provided, one year after the maturity thereof as stated therein; except, no such instrument may be destroyed until one year after the maturity of the last extension thereof filed in the recorder's office.
55 ILCS 5/3-5014